The present invention is a method of making a magnetoresistive sensor for use in a magnetoresistive read device. In particular, the present invention is a method of making a magnetoresistive sensor having an improved bias layer and an improved spacer layer such that the sensor produces an efficient output voltage for a given applied sense current.
Magnetoresistive (MR) sensors or heads are used to read magnetically encoded information from a magnetic medium by detecting magnetic flux stored in the magnetic medium. During the operation of an MR sensor, a sense current is passed through the MR element of the sensor, causing a voltage drop across the MR element. The magnitude of the voltage drop is a function of the resistance of the MR element. The resistance of the MR element varies in the presence of a magnetic field. Therefore, as the magnitude of the flux from a medium transition passing through the MR element varies, the voltage drop across the MR element also varies. Differences in the magnitude of the magnetic flux from the medium entering the MR sensor can be detected by monitoring the voltage across the MR element.
An MR sensor will provide an approximately linear output when the magnetization vector M of the MR element and the current density vector J of the MR element form an angle of approximately 45 degrees. Permalloy, a typically MR element material and an alloy of nickel and iron (approximately 81% nickel and 19% iron) will naturally tend to form a magnetization vector along its long axis when it is formed into a long narrow strip. This alignment is enhanced by a magnetic field induced anisotropy formed during the deposition of the permalloy element. The current density vector J is also typically directed along the same axis. By forming a soft adjacent layer (SAL) or bias layer near the MR element and in a parallel plane to the plane of the MR element, the magnetization vector can be rotated up to 90 degrees with respect to the long axis. The amount of saturation inductance BS of the SAL or bias layer directly effects this angle. Once again, it is desirous for this bias angle to be approximately 45 degrees, for purposes of near-linear response of the sensor.
MR sensors of the SAL or bias layer design have three important layers. First, a magnetic layer with MR properties which generates an output voltage when its magnetization is rotated and a sense current flows through the layer. Second, a SAL or magnetic bias layer, with essentially no magnetoresistive properties or response. The SAL biases the MR magnetic layer from a rest position to a magnetized position. Due to the fields generated by the sense current in the various layers, and the magnetostatic coupling with the MR layer, magnetization in the SAL or bias layer is usually saturated along its hard magnetization direction. Third, a non-magnetic spacer layer is positioned between the two above described magnetic layers. The spacer layer breaks the ferromagnetic exchange coupling between the MR magnetic layer and the SAL allowing the magnetic layers to act as two distinct layers, rather than as one strongly coupled layer.
In order for an MR sensor to properly read information from a magnetic storage medium, several factors are important. First, as described above, the MR magnetic layer must be biased such that the magnetization vector M and the current density vector J form an angle of approximately 45 degrees. Second, it is critical to have as much of the sense current flowing through the MR magnetic layer of the sensor as possible. Third, a bias layer and/or a spacer layer with increased resistance will cause a reduced amount of shunting of the output voltage generated by the MR magnetic layer. Thus, it is important that the resistance of the SAL and the resistance of the spacer layer are significantly larger than the resistance of the MR magnetic layer. These three resistances are in parallel with one another, since these three layers are positioned side-by-side, or in a three layer stack. Maximizing the resistances of the SAL and the spacer layer will reduce their undesirable shunting effects, and thereby will generate an increase in the output voltage signal of the MR sensor.
It is, therefore, one object of the present invention to provide an MR sensor which includes a properly biased MR magnetic layer, i.e., the magnetization vector M and the current density vector J form an angle of approximately 45 degrees. It is another object of the invention to provide an MR sensor which maximizes the amount of sense current which flows through the MR magnetic layer of the MR sensor and which has less shunting of its output voltage by the layers in the sensor xe2x80x9cstack,xe2x80x9d thereby maximizing the output voltage signal of the MR sensor.
A method of making a magnetoresistive sensor which detects information from a storage medium, such as a magnetic disc, and which provides an output voltage to a auxiliary circuitry is disclosed. The method comprises sputtering a bias layer (also known as a Soft Adjacent Layer (SAL)) in a sputtering gas mixture of nitrogen and argon. A spacer layer is also formed in a sputtering gas mixture of nitrogen and argon. Finally, an MR magnetic layer is formed. The spacer layer is positioned between the bias layer and the MR magnetic layer. The output voltage is provided to auxiliary circuitry when a bias current flows through the MR magnetic layer.
In one preferred embodiment, tantalum is vacuum sputter-deposited in a sputtering gas mixture of nitrogen and argon forming the spacer layer, while a Sendust-type alloy is sputter-deposited in a sputtering gas mixture of nitrogen and argon forming the bias layer.